The present invention relates to a belt for a continuously variable transmission, in which a par of left and right ring slots defined in each of a large number of metal elements are supported on a pair of left and right metal ring assemblies each formed of a plurality of endless metal rings laminated one on another, respectively, the belt being wound around a drive pulley and a driven pulley to transmit a driving force.
There are such belts for continuously variable transmission conventionally known from Japanese Patent Publication No.63-40979 and U.S. Pat. No. 4,915,677, in which in order to ensure that left and right V-faces of a metal element are brought into close contact with V-grooves of a pulley with uniform surface pressure to prevent the generation of an uneven wear, upward-directed recesses are defined at laterally opposite ends in the vicinity of the V-faces at a lower edge of an element body, so that the element body is easily flexed vertically at locations corresponding to the recesses.
In the conventionally known belt, however, when the V-faces of the metal element receive a compressive load from the V-grooves of the pulley, the V-faces are moved with the angle varied, rather than in parallel to each other. For this reason, upper or lower portions of the V-faces are put into uneven abutment against the V-grooves of the pulley and hence, it is difficult to necessarily effectively overcome an uneven wear. Another problem is that when a downward load is applied to saddle surfaces of the metal element by the tension of the metal ring assembly, the distribution of a bending load on the saddle surfaces is uneven laterally, resulting in a reduced durability of the metal element.
The present invention has been accomplished with the above circumstances in view, and it is an object of the present invention to enhance the durability of the metal element by devising a shape of a lower edge of the element body of the metal element.
To achieve the above object, according to the present invention, there is provided a belt for a continuously variable transmission, in which a pair of left and right ring slots defined in each of a large number of metal elements are supported on a pair of left and right metal ring assemblies each formed of a plurality of endless metal rings laminated one on another, respectively, the belt being wound around a drive pulley and a driven pulley to transmit a driving force, the metal element comprising a neck provided between the pair of left and right ring slots, an ear integrally connected to an upper portion of the neck, an element body integrally connected to a lower portion of the neck, a pair of left and right saddle surfaces formed on an upper surface of the element body to support a lower surface of the metal ring assembly, a pair of left and right V-faces formed at laterally opposite ends of the element body to abut against both of the pulleys, and a pair of left and right recesses defined in a lower edge of the element body and depressed upwards, characterized in that when an upper end of the V-face is represented by a; a lower end of the V-face is represented by b; an inner end of the saddle surface is represented by c; and an outer end of the saddle surface is represented by d, a first line on the lower edge of the element body is determined, and a second line straightforwardly connecting the lower end b of the V-face and the inner end c of the saddle surface is determined, so that when a downward load is applied from the metal ring assembly to the outer end d of the saddle surface, the folding-resistant strength of the element body is uniform laterally; and a position of the recess is determined in the vicinity of a point e of intersection of the first and second lines, the lower edge of the element body being defined by the first line inside the recess and by the second line outside the recess.
With the above arrangement, the first line inside the recess in the lower edge of the element body of the metal element is determined, so that when the downward load is applied from the metal ring assembly to the outer end d of the saddle surface, the folding-resistant strength of the element body is uniform laterally. Therefore, it is possible to prevent the stress from being concentrated on a portion of the element body to reduce the durability. In addition, the second line outside the recess in the lower edge of the element body of the metal element is determined, so that the lower end b of the V-face and the inner end c of the saddle surface are connected straightforwardly to each other. Therefore, even if a load is applied from the V-grooves of the pulley to the metal element, a surplus moment can be prevented from being generated on the element body or the saddle surface. Further, it is possible to ensure a coefficient of friction between the V-grooves and the V-faces, and to effectively prevent the generation of an abnormal wear, by defining the point of intersection of the first and second lines, so that the angle of the V-faces of the metal element is not varied.
In addition to the above arrangement, there is provided a belt for a continuously variable transmission, wherein a triangle formed by the upper end a of the V-face, the lower end b of the V-face and the inner end c of the saddle surface is an isosceles triangle in which the lengths of a side ca and a side cb are equal to each other.
With the above arrangement, the triangle formed by the upper end a of the V-face, the lower end b of the V-face and the inner end c of the saddle surface is the isosceles triangle and hence, the V-faces can be moved in parallel to each other by loads applied from the V-grooves of the pulley to the V-faces of the element body to ensure a sufficient coefficient of friction between the V-grooves and the V-faces, and to further effectively prevent the generation of an abnormal wear.